A configuration for multiple data stores, each referred as slice.
This configuration allows each underlying slice be configured with its
own specific configuration properties such as JDBC Driver or connection
user/password etc.
This configuration also extends by adding a DistributionPolicy that governs how new instances be distributed
among the slices.

getActiveSliceNames

Gets the active slice identifiers. This list is determined by the
configuration properties either by explicit listing in
openjpa.slice.Names property or by scanning
openjpa.slice.*.* properties.
The ordering of the slice identifiers is determined when they are
specified explicitly in openjpa.slice.Names property or
ordered alphabetically when found by scanning the properties.
This list always returns the identifiers that are active, slices
that can not be connected to are not included in this list.